Chemstation ISTD (internal standard) problems

[chromanator]

I am having difficulty establishing accurate ISTD reports using Chemstation Rev.A.10.02 on a HP 5890(II) with FID detector

When reporting a known sample concentration in external standard mode (ESTD) the quantification is quite good (approx. 5% error) [Calibration table correlation coefficient 0.995]. However, when swapping to ISTD report the error jumps 100%.

Internal standards were accurately added to each level on the 5 level calibration table and most peaks areas are nearly identical, one is 25% lower (level one - lowest value). S/N ratio is well above LOQ.

Additionally, Chemstation alert warning states more IS are required.

Would this peak area variabilty matter, in other words, must the slope of the IS calibration graph = 0 ?

Any suggestions to where this problem may lie would be most appreciated.

[AICMM]

chromanator,

Delete the area for that level and see if that helps.

Best regards.

[chromanator]

Hi AICMM,

Thanks for this advice, I was about to do so but found I could manually change the ISTD amount for all levels to the correct amount (one concentration only), as Chemstation automatically defauts the ISTD level values with the Calibration compound level concentrations.